In general, as shown in FIG. 6, a chain or belt transmission device for valve timing in an internal combustion engine, or for transmitting rotational power in another drive mechanism, includes a chain or belt C, which transmits power from a driving sprocket or pulley S1 to one or more driven sprockets or pulleys S2. The transmission includes a pivotally mounted, movable sliding contact guide Ga, which cooperates with a tensioner T, and a fixed sliding contact guide Gb. The movable guide and the fixed guide are attached to a frame E of the engine or other drive mechanism by suitable pins P, or by bolts or similar mountings. The guides make sliding contact with the chain or belt C, and prevent vibration of the chain or belt both in the plane of its traveling path (which is usually vertical), and in the transverse direction.
FIG. 7 shows a plastic movable guide 500, of the kind disclosed in the specification of Japanese Patent Application No. 382798/2000. The guide 500 comprises a guide body 510, including a shoe 511 having a front surface of which a chain, belt or other flexible power transmission medium C slides, and a plate-receiving portion 512, extending along the longitudinal direction of the guide on the back side of the shoe 511. The shoe and plate-receiving portions are integrally molded as a unit from a synthetic resin. The guide also includes a reinforcing plate 520 composed of a rigid material such as a rolled sheet material, a fiber-reinforced resin or the like, which reinforces the guide body 510. The plate is fitted into a slot 512a opening at an edge of said plate-receiving portion 512, facing away from the shoe and extending along the longitudinal direction of the guide.
A mounting hole 512b is provided in a boss 512c formed on the plate-receiving portion 512 adjacent one end of the guide body. The mounting hole allows the guide to be mounted on the frame of an engine or other machine. A hole 521 is also provided in the reinforcing plate adjacent one end thereof. When the reinforcing plate is inserted into the slot in the plate-receiving portion of the guide body, holes 521 and 512 are in register with each other so that they can both fit onto a pivot pin P, or on a mounting bolt or the like.
A plurality of reinforcing ribs 512d, reinforce the guide body. A tensioner-contacting portion 512e is formed on the plate-receiving portion adjacent the end of the guide body remote from the mounting hole 512b. The tensioner-contacting portion makes contact with the plunger of a tensioner T (FIG. 6), mounted on the frame of the engine E, to control tension in the power transmission medium.
The guide body 510 is produced by integrally molding the shoe 511 and the plate-receiving portion 512 as a unit from a synthetic resin. Accordingly, the chain or other flexible transmission medium slides along the guide body itself, and it is not necessary to provide a separate shoe. Thus the number of parts, and the number of production steps, is reduced. Further, since the reinforcing plate 520 is fitted into the slot 512a, the bending rigidity, toughness, and strength of the guide are significantly improved.
The reinforcing plate 520 is produced by pressing a rolled steel sheet or molding a fiber reinforced resin. However, the practical limit to the thickness of the reinforcing plate is about 4.5 mm. Consequently, it is not possible to improve the bending rigidity, toughness, and strength of the entire guide beyond what is afforded by a plate having a thickness of about 4.5 mm, and there is no room for increasing the largest allowable load in a conventional movable guide.
The reinforcing plate 520 substantially bears the load exerted as a result of tension in the chain C. As shown in FIG. 8, the reinforcing plate 520 is unstable in the direction of the width of the guide. Falling down as shown in FIG. 9(b), or “guide torsion” as shown in FIG. 10(b), are liable to occur, so that traveling movement of the chain becomes unstable.
As shown in FIG. 8, when the reinforcing plate 520 is produced by pressing a rolled steel sheet or the like, a portion F1 of the edge of the reinforcing plate may not be accurately perpendicular to the side faces, and the load imparted to the plate by the tension in a chain must be borne by the narrow remaining portion F2. As a result, excessive pressure is applied to portion F2. Moreover, the chain tends to move widthwise off the guide, which causes instability in the movement of the chain. The contact portion 522 is liable to wear out prematurely, and the frame mounting hole 512b in the guide body 510 and the hole 521 in the reinforcing plate 520 are also liable to wear out prematurely due to instability. Thus, a reinforcing plate produced by pressing a rolled steel sheet cannot be used satisfactorily under the heavy load conditions encountered in an engine, such as a diesel engine, in which two timing chains are arranged in parallel to each other.
In order to meet high load imposed on the tensioner by the tension of a chain under the rigorous transmission conditions encountered in an engine, the modulus the guide may be increased by increasing the height H of the guide body 510 and reinforcing plate 520 as shown in FIG. 6. The height H may be increased so that the plate-receiving portion of the guide body is as shown by the broken line in FIG. 6. However, the space available in the engine limits the height H, and a reinforcing plate 520 having increased height cannot be used in engines designed in accordance with the recent trend toward increased load and greater compactness.
Accordingly, an object of the invention is to solve one or more of the above-mentioned problems. Another object of the invention is to provide a movable guide for that can maintain stable travel of the transmission medium, and avoid running of the transmission medium off the guide in the widthwise direction. Other objects are to increase load capacity and compactness in a transmission device by significantly increasing bending rigidity, toughness, strength, and wear-resistance of the entire guide, and to prevent falling down of the guide and guide torsion.